1. Field of the Invention
The present invention relates to a magnetic head for use in a tape recorder such as an audio tape recorder, video tape recorder and digital audio tape recorder, and other magnetic recording and reproducing apparatus for a hard disk, floppy disk, magnetic card and the like, and more particularly relates to a magnetic head having a chromium nitride protective film and to a method of manufacturing the same.
2. Description of the Prior Art
In a general magnetic recording and reproducing apparatus, a magnetic head is used for recording, reproducing, and erasing data by sliding a magnetic recording medium such as a magnetic tape or magnetic disk on a top surface of the magnetic head. In such a case, a magnetic head is involved with a problem that the sliding movement of the head in contact with a recording medium inevitably causes frictional wear of the top surface of the head, which eventually leads to the deterioration of electromagnetic conversion characteristics of the magnetic head performance.
In attempts to eliminate such a problem, there have been made various proposals. For example, in the Japanese Patent Publication No. 56-1682 (published in 1981), there is disclosed a method where a boron imparting material is applied to the sliding surface of the magnetic head, which is then subjected to an annealing process to form a boron diffused layer thereon to substantially harden the sliding surface of the head with an improvement in wear resistance.
Another method has been proposed in the Japanese Patent Publication No. 55-12652 (published in 1980) where metal hardening atoms are implanted by ion implantation into the sliding surface of the magnetic head to harden the sliding surface, whereby improvement in wear resistance is achieved.
Further, there has been proposed still another method where improvement in wear resistance of the magnetic head is achieved by coating a thin film having a high degree of hardness on the sliding surface of the magnetic head. For example, in the Japanese Patent Unexamined Laid-Open 267363/1991, disclosed is a method in which a thin film of boron nitride is provided on a surface of an intermediate thin layer which is formed on the sliding surface of the magnetic head. The intermediate thin layer contains at least one kind of element of group IIIb, group IVa and group IVb elements.
However, these methods involve the following problems. That is, in the method which comprises a process of thermal diffusion of a boron material, as well as in the method which comprises a process of ion implantation, the control operation of the process must be strictly effected for adjusting the temperature, cooling velocity, and the like, which results in higher production cost. Further, the use of a high temperature treatment and the impact of ions may adversely affect the interior of the magnetic head.
With the method which comprises a process of forming a thin film of boron nitride, there is a problem involved in that a two-layer structure is required. That is, the boron nitride film is formed on an intermediate thin layer, which naturally results in lower productivity. Another problem is that, for the purpose of an improvement in wear resistance, the thin film coating is often made thicker than 0.1 .mu.m in its total thickness, so that the thin film of the head defines a spacing between the head and a recording medium. Hence, the spacing virtually causes a loss due to uneven wear of the sliding surface, deteriorating the electromagnetic conversion characteristics of the head. Even a degree of film thickness of more than 0.1 .mu.m is not sufficient to achieve a good wear resistance.
Accordingly, the present inventor attempted to form a protective film made of chromium nitride on a sliding surface of a magnetic head by a method using a reactive high-frequency magnetron sputtering technique. Then the inventor discovered the fact that this approach could provide a film coating having no adverse influence on the electromagnetic conversion characteristics of the head with its thickness less than 0.1 .mu.m, which still has excellent wear resistance. In the tests of driving the magnetic head with a magnetic tape having its magnetic layer composed of an iron oxide magnetic substance, the protective film coated on the sliding surface of the magnetic head exhibited an excellent wear resistance, having an endurance in driving for more than 1000 hours.
However, in the driving tests using a magnetic tape having its magnetic layer containing a chrome oxide magnetic substance, since the chrome oxide has a high abrasive force against the magnetic head, there occurred many spot-like peelings of the protective film of chromium nitride on the sliding surface of the head in driving for 100 hours, and the area of the peeling portion was increased with time lapse of the driving to an extent that the protective film of chromium nitride was peeled off over an area of about one half of the sliding surface area of the head in a time period of 500 hours.
Further, there has not been known yet in the art any protective coating film for magnetic heads which can exhibit excellent wear resistance as well stand a driving test for more than 1000 hours against a magnetic tape having its magnetic layer composed of a chrome oxide magnetic substance.